You want to invest $10,000 for 20 years at 10 % interest compounded quarterly. How much money will you have at the end of the 20 years?
Solve 
Step 
i = 0.10 ÷ 4 = 0.025 
k = 4, r = 0.10, Quarterly means 4 times a year 
FV = PV(1 + i)^{kn} 
PV = 10,000, n = 20 years 
FV = 10,000(1 + 0.025)^{4(20)} 
Find the Future Value 
FV = 10,000(1.025)^{80} » 72,095.68 

You would have $72,095.68 after 20 years. (before taxes)  
Hint: don't round until you are completely finished with your calculations. 